An image sensor irradiates an object to be read using irradiation light emitted by a light source incorporated in a casing, and light reflected by the object to be read is focused through a focusing optical system, such as a lens, onto a photoelectric conversion element, and image data is obtained (for example, see Patent Literature 1).
The image sensor described in Patent Literature 1 is equipped with a first casing that retains a lens and a sensor board, and a second casing that retains a light source board and glass.